gravity varies with elevation and latitude, to be any more precise one would have to take these factors into account, and 9.80665 is a convention instituted after newton's time anyway. also, a negative sign is only an arbitrary consequence of a directional choice. also, in any scientific context, units composed of m, s, and kg are assumed unless otherwise stated, and a number is just as meaningless with units and no context as it is without either anyways. here, there is context, ~9.81 is the most easily...